PubMedCentral-PMC5102500.pdf

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Association of Cervical Effacement With the Rate of Cervical

Change in Labor Among Nulliparous Women

Elizabeth S. Langen, M.D., Steven J. Weiner, M.S., Steven L. Bloom, M.D., Dwight J. Rouse, M.D., Michael W. Varner, M.D., Uma M. Reddy, M.D., M.P.H., Susan M. Ramin, M.D., Steve N. Caritis, M.D., Alan M. Peaceman, M.D., Yoram Sorokin, M.D., Anthony Sciscione, D.O., Marshall W. Carpenter, M.D., Brian M. Mercer, M.D., John M. Thorp Jr., M.D., Fergal D. Malone, M.D., Jay D. Iams, M.D., and for the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network*

From the Departments of Obstetrics and Gynecology of Stanford University, Stanford, CA (E.S.L.); University of Texas Southwestern Medical Center, Dallas, TX (S.L.B.); University of Alabama at Birmingham, Birmingham, AL (D.J.R.); University of Utah Health Sciences Center, Salt Lake City, UT (M.W.V.); The University of Texas Health Science Center at Houston-Children’s Memorial Hermann Hospital, Houston, TX (S.M.R.); University of Pittsburgh, Pittsburgh, PA (S.N.C.); Northwestern University, Chicago, IL (A.M.P.); Wayne State University, Detroit, MI (Y.S.); Drexel University, Philadelphia, PA (A.S.); Brown University, Providence, RI (M.W.C.); MetroHealth Medical Center- Case Western Reserve University, Cleveland, OH (B.M.M.); University of North Carolina at Chapel Hill, Chapel Hill, NC (J.M.T.); Columbia University, New York, NY (F.D.M.); The Ohio State University, Columbus, OH (J.D.I.); and the George Washington University Biostatistics Center, Washington, DC (S.J.W.); and Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD (U.M.R.)

Abstract

Objective—To assess the association of cervical effacement with the rate of intrapartum cervical change among nulliparous women.

Methods—We conducted a secondary analysis of a prospective trial of intrapartum fetal pulse oximetry. For women who had vaginal deliveries, interval censored regression was used to estimate the time to dilate at one centimeter intervals. For each given centimeter of progressive cervical dilation, women were divided into those who had achieved 100% cervical effacement and those who had not. The analysis was performed separately for women in spontaneous labor and those who were given oxytocin.

Results—Three thousand nine hundred two women were included in this analysis, 1,466 (38%) who underwent labor induction, 1,948 (50%) who underwent labor augmentation (combined for the analysis), as well as 488 (13%) who labored spontaneously. For women in spontaneous labor, the time to dilate 1 cm was shorter for those who were 100% effaced starting at 4 cm of cervical

Corresponding Author: Elizabeth S. Langen, MD, Obstetrics and Gynecology, Floor 9 Room 109 VVWH, 1540 W. Hospital Drive, SPC 4264, Ann Arbor, MI 48109-4264, (650) 799-8784, [email protected].

*For a list of other members of the NICHD MFMU Network, see Appendix 1 online at http://links.lww.com/xxx.

HHS Public Access

Author manuscript

Obstet Gynecol

. Author manuscript; available in PMC 2017 March 01.

Published in final edited form as:

Obstet Gynecol. 2016 March ; 127(3): 489–495. doi:10.1097/AOG.0000000000001299.

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dilation (P = 0.01 to P < 0.001). For women who received oxytocin, the time to dilate 1 cm was shorter for those who were 100% effaced throughout labor (P < 0.001).

Conclusion—The rate of cervical dilation among nulliparous women is associated with not only the degree of cervical dilation, but also with cervical effacement.

Clinical Trial Registration—ClinicalTrials.gov, www.clinicaltrials.gov, NCT00098709.

Précis

Achievement of 100% cervical effacement is associated with a shorter median time of dilation among nulliparous women.

Introduction

In recent years, the Consortium on Safe Labor (CSL) labor curves have replaced the traditional labor curve proposed by Friedman (1–3, 4). The importance of understanding normal labor progression was highlighted by Rouse and colleagues in 1999 when they challenged the idea that arrest of labor could be diagnosed after only 2 hours of inadequate cervical change (5). Rouse and colleagues found that 60% of women who were given 2 additional hours to demonstrate cervical change went on to deliver vaginally. This observation highlighted that an inappropriate model of normal labor can lead to an over diagnosis of arrest disorders of labor and subsequently unnecessary cesarean deliveries. The American College of Obstetrics and Gynecology and the Society for Maternal-Fetal Medicine consensus statement on the Safe Prevention of the Primary Cesarean Delivery recommends using the CSL labor curves to define normal labor progress (6).

The CSL labor curve emphasizes the notion that active labor may not begin until 6 cm of cervical dilation. The CSL labor curve does not specifically address the role of cervical effacement in predicting normal rates of cervical change. Cervical effacement, however, has been used by many authors as a traditional part of the definition of active labor (7) and clinical experience would suggest that cervical effacement plays a role in labor progress. The current study assesses the association of cervical effacement with the rate of intrapartum cervical change among nulliparous women.

Materials and Methods

We conducted a secondary analysis of a prospective trial of fetal pulse oximetry conducted by the National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network (8). In the original study, women were eligible to participate if they were nulliparous with a singleton, cephalic, living fetus at or beyond 36 weeks of gestation. Exclusion criteria included a planned cesarean delivery, maternal temperature ≥38°C, maternal HIV or hepatitis infection, maternal heart or renal disease and diabetes mellitus requiring insulin. Women were enrolled with cervical dilations between 2 and 6 cm. Labor was managed according to the usual clinical practice at the participating centers. The original study was approved by the institutional review board at each participating Maternal-Fetal Medicine Units Network center and written informed consent was obtained from each participant. Data were collected by trained research nurses.

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For the current study, we included all participants who had a vaginal delivery of a live-born infant. There were no stillbirths. A separate analysis included those participants who had a cesarean delivery for an arrest disorder. We abstracted data on patient race, body mass index, use of epidural anesthesia, use of oxytocin for labor induction or augmentation, use of cervical ripening agents, and details of labor progression including cervical dilation and effacement at each exam.

When comparing demographic and other patient characteristics between those with induced or augmented labor to those with spontaneous labor, the Wilcoxon rank-sum test was used to compare continuous variables, and categorical variables were compared by means of the chi-square or Fisher's exact test, as appropriate. Analyses are presented separately for those with induced or augmented labor and those with spontaneous labor. Cervical effacement was recorded as a percentage of effacement (0–100%). Given that measurements of cervical effacement can often vary significantly by observer (9, 10) as well as the presumed clinical importance of achieving 100% cervical effacement, women were stratified into those who had achieved 100% cervical effacement and those who had not at each cervical exam. We used interval-censored regression to estimate the time to progress from one integer centimeter dilation to the next, assuming a log-normal distribution (11). Since cervical exams are often irregularly spaced, an individual may have progressed several centimeters of dilation from one exam to the next. Therefore, interval-censoring allows an estimation of the time between any two one-centimeter measurements (e.g., from 4 cm to 5 cm), even when

those precise measurements were not observed for all patients. The median, 5th percentile,

and 95th percentile were calculated for the time to progress between every two successive

dilations, and the times for those at 100% effacement versus less than 100% effacement were compared with a Wald test using procedure LIFEREG in SAS Version 9.3. Using these same methods, a model was constructed with the covariates of 100% cervical effacement (yes vs. no), use of regional anesthesia (yes vs. no), maternal BMI, age, and race (white vs. all others). To calculate the cumulative time from 4 cm, 5 cm, and 6 cm to complete cervical dilation, right-censored regression assuming a log-normal distribution was used, with effacement assessed at the initial cervical dilation. Among women whose labor was induced, a model was constructed with additional terms for mechanical ripening, medical ripening, and their interactions with 100% cervical effacement. Finally, these analyses were repeated for the women who had cesarean deliveries for arrest disorders.

Results

The original trial randomized 5,341 women. Of these, 1,439 women had a cesarean delivery, leaving 3,902 women with vaginal deliveries in this analysis. There were no stillbirths. The current cohort included 1,466 (38%) women who underwent labor induction and 1,948 (50%) who underwent labor augmentation with oxytocin (combined for the analysis), as well as 488 (13%) women who labored spontaneously. Women in spontaneous labor were different from those women who were augmented or induced in most baseline

characteristics, though the absolute magnitude of the differences was small (Table 1). Missing information on cervical effacement was rare. Fewer than 1% of cervical examinations were missing an effacement measurement.

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For women who received oxytocin during labor, the time to dilate from each centimeter to the next was significantly shorter for women who were 100% effaced compared with those who were not (Table 2). For women who had spontaneous labor, the time to dilate from 2 to 3 cm and 3 to 4 cm did not differ by effacement, while the time to dilate from 4 to 5 cm, 5 to 6 cm, 6 to 7 cm, 7 to 8 cm, 8 to 9 cm and 9 to 10 cm was significantly shorter for those who were 100% effaced vs. those who were not (Table 2). When potential confounders including maternal race, age, BMI at the time of delivery, and use of regional anesthesia were

considered in the model, the trend remained unchanged (Table 3).

For women who received oxytocin during labor, the time to reach 10 cm of cervical dilation from 4, 5, and 6 cm respectively was longer for those women who had not yet achieved 100% cervical effacement at the starting dilation. For women in spontaneous labor, this was true for 4 and 5 cm of cervical dilation. However, the 100% cervical effacement at 6 cm dilation was not associated with a significantly shorter duration to reach 10 cm dilation (Table 4).

Among women whose labors were induced, 370 (25.2%) were medically ripened and 243 (16.6%) were mechanically ripened. Medical ripening shortened the time to dilate from 6 to 7 cm beyond the effect of 100% effacement (p=0.03), but not at other dilations. Mechanical ripening shortened the time to dilate from 9 to 10 cm beyond the effect of 100% effacement (p=0.01), but not at other dilations.

From the 1,439 women who had a cesarean delivery, we performed an analysis of the 985 who delivered by cesarean for an arrest disorder in the first (n=773) or second (n=212) stage of labor, despite the use of oxytocin. Those women with 100% effacement had consistently faster rates of cervical dilation compared with those at less than 100% (Tables 5–6).

Discussion

Labor is defined as “uterine contractions that bring about demonstrable effacement and dilation of the cervix.” (12) While labor involves both dilation and effacement, existing labor curves demonstrate only the rate of cervical change in relationship to cervical dilation (1–4). We sought to investigate how cervical effacement might influence expectations of the rate of cervical change. In this large cohort of nulliparous women, the rate of cervical dilation in labor was significantly associated with achieving 100% cervical effacement.

Much attention has been paid to when the transition to active labor begins. The CSL data suggest that active labor may not begin until 6 cm (1, 6). This strict criterion, however, has been challenged by Cohen and Friedman who “discouraged the use of any specific degree of dilation for the identification of the active phase” (13). They argue that the timing of active labor depends on assessment of the individual patient, but is typically between 3 and 6 cm. Our observations suggest that combining the assessment of cervical dilation with cervical effacement may allow us to better define the beginning of active labor. If our findings are confirmed, future labor guidelines may wish to include the combination of cervical dilation and effacement when defining active labor.

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Our analyses consistently demonstrated that achievement of 100% cervical effacement was associated with faster labor progression. Even when the comparisons did not reach statistical significance, the trend was in this direction. The instances that were not statistically

significant occurred in those with spontaneous labor, which were a minority of our cohort. In particular, the availability of data at earlier dilations was scarce in this group, likely

secondary to fewer women in spontaneous labor having been admitted to labor and delivery prior to more advanced cervical dilations. Overall, these smaller numbers do limit our ability to comment on this group.

Strengths of this study include the prospective collection of data from a large number of nulliparous women from multiple institutions. However, measuring the rate of labor progress was not the focus of the study, and there was no protocol regarding the frequency of

examinations or the experience level of those performing them. The uneven frequency is partially addressed through our statistical methods, but potential observer errors are not. By separating women into those who were 100% effaced vs. not, we hoped to eliminate some of the inter-observer variability that is inherent in measuring cervical effacement (9, 10). This decision was designed to provide more-reproducible results, while allowing us to provide insight into how cervical effacement is associated with labor progression.

While those who have cesarean deliveries for arrest disorders have slower labor progression, we wished to address the basic question regarding cervical effacement in this group as well. Therefore, we repeated the analysis in this group and found that the pattern of more rapid cervical dilation was associated with achievement of 100% cervical effacement in these women as well. While the absolute range of time to dilate from one centimeter to the next may differ between those with a vaginal or cesarean delivery, the association between rate of cervical change and 100% cervical effacement was consistently observed.

Our study is applicable only to women who share characteristics with the women in the original study. We do not have data on multiparous women or diabetic women. Also, our analysis was limited to those who arrived at the hospital and agreed to participate in the randomized trial before reaching 7 cm dilation. Those missed would include women whose labor was progressing more quickly and therefore without sufficient opportunity to enroll in the trial. The result is an unknown lengthening of the time we report for labor progression. Lastly, those who chose to participate in the randomized trial may be different from those who did not.

Finally, our analysis combined women who had labor inductions with those who had labor augmentations. This was done because the distinction between these groups can be difficult to make and there is likely substantial overlap. The combination of these two groups is supported by the findings by Harper and colleagues who analyzed the labor progress of women with augmented and induced labors and found them to be similar (14).

Labor involves a complex process of both cervical dilation and effacement. As we strive to safely reduce the number of unnecessary cesarean deliveries, we hope that an understanding of how cervical effacement may impact the expected rate of cervical change in labor will allow clinicians to more appropriately diagnose arrest disorders.

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Supplementary Material

Refer to Web version on PubMed Central for supplementary material.

Acknowledgments

The authors thank Allison Todd, M.S.N., R.N. for protocol development and coordination between clinical research centers; Elizabeth Thom, Ph.D. for protocol development, data management and statistical analysis; and Kenneth J. Leveno, M.D. and Catherine Y. Spong, M.D. for protocol development and oversight.

Supported by grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) [HD21410, HD27860, HD27869, HD27915, HD27917, HD34116, HD34136, HD34208, HD40485, HD40500, HD40512, HD40544, M01 RR00080 (NCRR); HD40545, HD40560, and HD36801]. Comments and views of the authors do not necessarily represent views of the NICHD.

References

1. Zhang J, Troendle JF, Yancy MK. Reassessing the labor curve in nulliparous women. Am J Obstet Gynecol. 2002; 187(4):824–828. [PubMed: 12388957]

2. Zhang J, Landy HJ, Branch DW, Burkman R, Haberman S, Gregory KD, et al. Contemporary patterns of spontaneous labor with normal neonatal outcomes. Obstet Gynecol. 2010; 116(6):1281– 1287. [PubMed: 21099592]

3. Laughon SK, Branch DW, Beaver J, Zhang J. Changes in labor patterns over 50 years. Am J Obstet Gynecol. 2012; 206(5):419.e1–419.e9. [PubMed: 22542117]

4. Friedman EA. The graphic analysis of labor. Am J Obstet Gynecol. 1954; 68:1558–1575.

5. Rouse DJ, Owen J, Hauth JC. Active-phase labor arrest: Oxytocin augmentation for at least 4 hours. Obstet Gynecol. 1999; 93(3):323–328. [PubMed: 10074971]

6. Caughey AB, Cahill AG, Guise JM, Rouse DJ. ACOG, SMFM. Safe prevention of the primary cesarean delivery. Am J Obstet Gynecol. 2014; 210(3):179–193. [PubMed: 24565430]

7. Laughon SK, Zhang J, Troendle J, Sun J, Reddy UM. Using a simplified Bishop score to predict vaginal delivery. Obstet Gynecol. 2011; 117(4):805–811. [PubMed: 21383643]

8. Bloom SL, Spong CY, Thom E, Varner MW, Rouse DJ, Weininger S, et al. Fetal pulse oximetry and cesarean delivery. N Engl J Med. 2006; 355(21):2195–2202. [PubMed: 17124017]

9. Holcomb WL, Smeltzer JS. Cervical effacement: variation in belief among clinicians. Obstet Gynecol. 1991; 78(1):43–45. [PubMed: 2047066]

10. Huhn KA, Brost BC. Accuracy of simulated cervical dilation and effacement measurements among practitioners. Am J Obstet Gynecol. 2004; 191:1797–1799. [PubMed: 15547567]

11. Vahratian A, Troendle FJ, Seiga-Riz AM, Zhang J. Methodological challenges in studying labour progression. Paediatr Perinat Epidemiol. 2006; 20:72–78. [PubMed: 16420344]

12. Cunnigham, GF.; Leveno, KJ.; Bloom, SL.; Spong, CY.; Dashe, JS.; Hoffman, BL., et al. Williams Obstetrics. 24th. New York (NY): McGraw Hill Education; 2014.

13. Cohen WR, Friedman EA. Perils of the new labor management guidelines. Am J Obstet Gynecol. 2015; 212(4):420–427. [PubMed: 25218127]

14. Harper LM, Caughey AB, Odibo AO, Roehl KA, Zhao Q, Cahill AG. Normal progress of induced labor. Obstet Gynecol. 2012; 119(6):1113–1118. [PubMed: 22569121]

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Table 1

Patient demographics and labor characteristics *

Characteristic Overall

(n=3.902)

Induced/Augmented (n=1,466/1.948)

Spontaneous

(n=488) p-value†

Maternal race <0.001

Black or African American 1,190 (30.5%) 1,051 (30.8%) 139 (28.5%) White 2,041 (52.3%) 1,856 (54.4%) 185 (37.9%) Other 671 (17.2%) 507 (14.9%) 164 (33.6%) Ethnicity

Hispanic/Latina 952 (24.4%) 756 (22.1%) 196 (40.2%) <0.001

Maternal age (years) 23.0 ± 5.2 23.3 ± 5.3 21.6 ± 4.6 <0.001

BMI at end of pregnancy (kg/m2₎

<0.001

18.5–24.9 500 (12.9%) 405 (12.0%) 95 (19.6%) 25–29.9 1,452 (37.5%) 1,263 (37.3%) 189 (39.1%) 30–34.9 1,152 (29.8%) 1,026 (30.3%) 126 (26.0%) >=35 767 (19.8%) 693 (20.5%) 74 (15.3%) Mean/s.d. 30.9 ± 5.9 31.1 ± 5.9 29.8 ± 5.8

Gestational age at delivery (weeks)

39.7 ± 1.3 39.7 ± 1.3 39.5 ± 1.2 <0.001

Regional anesthesia 3,695 (94.7%) 3,302 (96.7%) 393 (80.5%) <0.001 Initiated before

randomization

3,349 (85.8%) 3,027 (88.7%) 322 (66.0%) <0.001

Delivery method 0.002

Spontaneous vaginal 3,122 (80.0%) 2,708 (79.3%) 414 (84.8%) Forceps 456 (11.7%) 403 (11.8%) 53 (10.9%) Vacuum 324 (8.3%) 303 (8.9%) 21 (4.3%)

Dilation at first exam (cm) 3 [2–4] 2 [1–3] 4 [3–4] <0.001

Effacement at first exam (%) 75 [50–90] 75 [50–90] 90 [80–100] <0.001

Number of cervical exams per patient

6 [5–8] 7 [5–8] 5 [4–6] <0.001

Time from one exam to the next (mins)

89 [52–140] 90 [52–140] 80 [45–125] <0.001

Birth weight (grams) 3,315 ± 445 3,323 ± 448 3,265 ± 421 0.001

BMI, body mass index *

Data are mean ± standard deviation, n (%), or median [interquartile range] †

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T ab le 2

Median time (minutes) to increase to the ne

xt centimeter cervical dilation, comparing those completely ef

faced with those less than completely ef

faced. * Induced/A ugmented Labor (n=3,414) Spontaneous Labor (n=488) Cer vic al dilatio n inter v a l (cm) N † 100% effaced median (5th–95th _percentile) N †

<100% effaced median (5th–95th _percentile) p-v alue ‡ N † 100% effaced median (5th–95th _percentile) N †

<100% effaced median (5th–95th _percentile) p-v alue ‡ 2–3 90 34.8 (5.2–232.6) 1655 90.6 (13.6–605.5) <0.001 16 39.6 (10.2–154.1) 77 37.6 (9.7–146.2) 0.89 3–4 293 38.5 (6.9–216.5) 2385 84.1 (15.0–472.6) <0.001 47 32.7 (8.0–134.5) 180 40.2 (9.8–165.5) 0.39 4–5 707 40.8 (6.9–242.3) 2533 80.6 (13.6–477.9) <0.001 137 41.4 (8.0–215.2) 258 59.5 (11.4–309.0) 0.01 5–6 1194 38.2 (6.0–243.4) 2191 72.7 (11.4–463.7) <0.001 223 32.1 (6.0–173.5) 243 56.7 (10.5–306.1) <0.001 6–7 1720 31.5 (4.9–203.1) 1693 61.6 (9.5–397.7) <0.001 321 33.7 (6.8–168.1) 167 57.2 (11.5–285.2) <0.001 7–8 1974 24.5 (3.4–174.4) 1440 52.2 (7.3–371.6) <0.001 339 27.0 (4.6–157.9) 149 43.6 (7.5–254.8) <0.001 8–9 2285 19.2 (2.6–140.2) 1129 44.8 (6.1–327.0) <0.001 376 22.4 (3.8–130.4) 112 41.8 (7.2–243.4) <0.001 9–10 2738 17.5 (2.3–132.2) 676 44.2 (5.9–333.2) <0.001 427 15.9 (2.4–106.4) 61 47.4 (7.1–317.8) <0.001 * Ef

facement assessed at the earlier of an

y tw

o successi

v

e e

xaminations.

† Represents the number of w

omen with a

v

ailable cervical measurement data at the specif

ied range of cervical dilation and le

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el of ef

facement. Note that the ef

facement w

as assessed at the earlier of an

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successi

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xaminations, and therefore may ha

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al if no e

xamination w

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‡ Compares those completely ef

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al-censored re

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T ab le 3

xt centimeter cervical dilation, comparing those completely ef

faced,

with adjustment for maternal body mass inde

x, race, age, and use of epidural anesthesia.

* Induced/A ugmented Labor (n=3,387) † Spontaneous Labor (n=484) † Cer vic al dilatio n inter v a l (cm) N ‡ 100% effaced median (5th–95th _percentile) N ‡

<100% effaced median (5th–95th _percentile) p-v alue § N ‡ 100% effaced median (5th–95th _percentile) N ‡

<100% effaced median (5th–95th _percentile) p-v alue § 2–3 90 36.2 (5.6–234.5) 1645 92.5 (14.3–598.8) <0.001 16 39.5 (10.8–143.7) 76 36.3 (10.0–132.4) 0.93 3–4 293 39.4 (7.2–216.5) 2363 85.4 (15.6–468.6) <0.001 47 33.6 (9.0–126.2) 179 39.4 (10.5–147.8) 0.23 4–5 703 42.5 (7.5–241.0) 2510 83.0 (14.6–470.9) <0.001 135 41.5 (8.2–210.4) 257 60.6 (12.0–307.0) 0.01 5–6 1186 40.1 (6.6–242.8) 2172 75.4 (12.5–456.3) <0.001 220 33.0 (6.3–171.9) 242 58.3 (11.2–303.6) <0.001 6–7 1705 32.4 (5.2–203.2) 1681 62.7 (10.0–394.1) <0.001 317 35.9 (7.7–167.7) 167 59.0 (12.6–276.0) <0.001 7–8 1956 25.2 (3.6–174.1) 1431 53.1 (7.7–367.6) <0.001 335 29.0 (5.3–158.8) 149 44.9 (8.2–245.4) 0.001 8–9 2264 19.6 (2.7–140.7) 1123 45.3 (6.3–324.7) <0.001 372 24.0 (4.4–131.3) 112 42.9 (7.8–234.5) <0.001 9–10 2713 17.9 (2.4–132.7) 674 44.8 (6.0–332.3) <0.001 423 16.5 (2.5–106.7) 61 48.4 (7.5–313.7) <0.001 * Ef

y tw

o successi

v

e e

xaminations.

† Thirty-one w

omen (27 with induced or augmented labor; 4 with spontaneous labor) are not included in this analysis due to missing data for maternal body mass inde

x.

‡ Represents the number of w

omen with a

v

el of ef

facement w

y tw

o

successi

v

e e

v

al if no e

xamination w

wer end itself.

§ Compares those completely ef

faced using interv

al-censored re

gression and a W

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T

ab

le 4

Median time (minutes) to reach 10 cm of cervical dilation from 4, 5, and 6 cm respecti

v

ely

, comparing those completely ef

faced v

ersus less than

completely ef

faced.

*

Induced/A

ugmented Labor

(n=3,414)

Spontaneous Labor

(n=488)

Cer

vic al

dilatio

n

change

(cm)

N

†

100%

effaced median (5th–95th percentil

e)

N

†

<100% effaced median (5th–95th percentil

e)

p-v

alue

‡

N

†

100%

effaced median (5th–95th percentil

e)

N

†

<100% effaced median (5th–95th percentil

e)

p-v

alue

‡

4–10

591

304.0

(122.1– 757.0)

1881

370.4

(148.8– 922.3)

<0.001

117

299.0

(144.2– 619.6)

192

340.1

(164.1– 704.8)

0.01

5–10

849

224.4 _(79.4– _634.2)

1139

255.3 _(90.3– _721.7)

<0.001

142

199.5 _(87.0– _457.7)

117

238.3

(103.9– 546.5)

0.005

6–10

1079

150.3 _(45.9– _492.7)

663

178.0 _(54.3– _583.3)

<0.001

230

145.6 _(52.5– _403.8)

84

167.9 _(60.5– _465.7)

0.07

* Ef

y tw

o successi

v

e e

xaminations. Each ro

w of the table includes only those w

omen with a cervical measurement at the starting dilation (i.e., 4, 5, or 6 centimeters).

omen with a

v

el of ef

facement. Ef

facement is classif

ied per the e

xamination at the start of the

dilation interv

al.

faced using right-censored re

gression and a W

(11)

A

uthor Man

uscr

ipt

A

uthor Man

uscr

ipt

A

uthor Man

uscr

ipt

A

uthor Man

uscr

ipt

T

ab

le 5

xt centimeter cervical dilation among 985 w

omen with induced or augmented labor who had a cesarean

deli

v

ery for dystocia, comparing those completely ef

faced.

*

Cer

vical

dilation inter

v

al

(cm)

N

†

100% effaced

median

(5th–95th percentile)

N

†

<100% effaced

median

p-v

alue

‡

2–3

28

50.0

(7.1–353.2)

601

111.4

(15.8–786.7)

0.007

3–4

89

48.6

(8.5–279.6)

741

102.4

(17.8–589.2)

<0.001

4–5

201

80.3

(15.8–407.1)

626

108.4

(21.4–549.8)

0.001

5–6

264

55.7

(9.2–335.9)

376

86.0

(14.3–518.3)

<0.001

6–7

290

46.8

(7.9–276.4)

180

78.5

(13.3–463.9)

<0.001

7–8

260

38.5

(6.5–227.6)

104

63.0

(10.7–372.3)

0.001

8–9

241

26.5

(4.4–158.4)

53

61.6

(10.3–367.8)

<0.001

9–10

199

32.5

(5.8–182.1)

13

100.5

(18.0–562.5)

<0.001

* Cesarean deli

v

ery for arrest disorders from both the f

irst and second stages of labor

. Ef

y tw

o successi

v

e e

xaminations.

omen with a

v

el of ef

facement w

y tw

o

successi

v

e e

v

al if no e

xamination w

wer end itself.

faced using interv

al-censored re

gression and a W

(12)

A

uthor Man

uscr

ipt

A

uthor Man

uscr

ipt

A

uthor Man

uscr

ipt

A

uthor Man

uscr

ipt

T

ab

le 6

xt centimeter cervical dilation among 974 w

omen who had a cesarean deli

v

ery for dystocia, comparing those

completely ef

faced v

ersus with those than completely ef

faced, with adjustment for maternal body mass inde

x, race, age, and use of epidural anesthesia.

*

Cer

vical

dilation inter

v

al

(cm)

N

†

100% effaced

median

N

†

<100% effaced

median

p-v

alue

‡

2–3

28

54.0

(8.0–364.0)

593

116.2

(17.2–783.3)

0.01

3–4

87

49.2

(8.6–280.6)

733

102.5

(18.0–583.9)

<0.001

4–5

197

82.1

(16.6–406.5)

620

109.6

(22.1–542.9)

0.002

5–6

259

58.2

(10.1–334.4)

372

88.8

(15.4–510.2)

<0.001

6–7

286

48.4

(8.5–276.6)

178

79.4

(13.9–453.5)

<0.001

7–8

256

39.5

(6.8–228.9)

103

63.1

(10.9–365.9)

0.003

8–9

237

26.4

(4.4–158.9)

53

61.5

(10.2–369.8)

<0.001

9–10

196

31.9

(5.6–180.4)

13

100.1

(17.7–565.6)

0.001

* Cesarean deli

v

ery for arrest disorders from both the f

irst and second stages of labor

. Ef

y tw

o successi

v

e e

xaminations. Body mass inde

x w

as una

v

ailable for 11 w

omen,

and as a result do not appear in this table. † Represents the number of w

omen with a

v

el of ef

facement w

y tw

o

successi

v

e e

v

al if no e

xamination w

wer end itself.

faced using interv

al-censored re

gression and a W